Structure of the digestive system
Before we talk about the microbiome, let’s lay a foundation for what a normal healthy digestive system looks like.
Once you put food in your mouth (which can we talk about this- it is estimated you will consume around 60 tons of food in your lifetime)1, your digestive system has already started working. You have enzymes in your mouth that begin the digestive process.
The food then moves into the stomach where stomach acid further breaks down the food you are eating into smaller and smaller particles. During this process, the body also begins the process of packaging some vitamins for absorption.
Out of the stomach, the food moves through the small intestines. This is where most of the final digestion and absorption occurs. The gallbladder (which holds a lot of the digestive enzymes) releases into the first part of the small intestines called the duodenum. The primary function of the rest of the small intestine is to package and absorb vitamins, minerals, and macronutrients (carbs, fats, proteins). The small intestine has a unique structure called villi and microvilli.
These folded structures in the intestine allow a larger absorptive area in a smaller space. The absorptive area of the small intestine if stretched out completely would be about the size of a tennis court2!! Once most of the absorption has occurred, the food finally moves into the large intestine where some absorption occurs (mostly water and salts) and the waste is packaged for removal (a bowel movement).
Balancing the Bacteria
On the interior of the structure of the digestive system (technically outside your body) is your microbiota (also known as your gut flora)- a combination of bacteria, archaea, and eukarya that lives in symbiotic relationship with you. This microbiota is comprised of 10x more bacterial cells than the number of human cells in your body1. When looking at the composition of the microbiota, one of most important components are probiotics, bacteria that are beneficial for us.
These probiotics are responsible for
- Preventing reproduction of pathogenic microflora
- Antagonistic effect on harmful microorganisms
- Strengthen the immune system
- Improve digestion
- Support intestinal motility
- Produce vitamin K
- Normalize cholesterol
- Production of short-chain fatty acids, specifically butyrate (anti-inflammatory and anti-cancer)13
Imbalanced bacteria can lead to
- Increased allergies due to inappropriate growth of immune system
- Increased risk of autoimmune diseases like Type 1 DM, MS, and Crohn’s disease10
- Increased risk of obesity11
- Decreased wound healing14
- Increased risk of depression17
Ultimately, to be healthy- it becomes a primary focus to keep the bacteria healthy and happy. The bacteria in your GI system can change as you change, so it important to be mindful of them (maybe even before birth)! It was originally believed that your microbiota was established at birth- but some studies are showing that this might begin while you are still in the womb3. During delivery, a majority of the bacterial colonization occurs. During a vaginal delivery, the infant receives bacteria from mom’s vagina as well as fecal bacteria (including Lactobacillus and Bifidobacterium ssp)4. Babies born via C-section may get different strains of bacteria, as their primary source of colonization comes from bacteria present on the skin (and only resemble mom’s microbiota by 41% vs 72% if vaginally born)4. These babies have higher levels of Staphylococcus, Corynebacterium, and Propionibacterium ss5. Babies born via C-section are more likely to have lower microbiota diversity compared to those that were born vaginally as well as a delayed colonization of certain beneficial bacteria. This has been shown to have a decreased maturation of Th1/Th2 immune response6.
The first 3 years of life appear to be the most critical in establishing a healthy gut microbiome. During this period, dietary factors play an important role. Breast milk contains high levels of beneficial bacteria (more than 700 different species of bacteria) as well as several components that feed healthy bacteria7.
Surprising, even the number of siblings and where you live make a difference in gut bacteria levels. Infants that have siblings are more likely to have higher levels of Bifidobacterium ssp than those who are single infants. Infants that live outside large cities, in more rural areas, have higher levels of Bifidobacterium than those that lived inside the city. It is suggested that there is a decreased need for antibiotics due to overgrowth of bad bacteria in those that have higher levels of Bifidobacterium8,9.
What can we do to protect a healthy microbiome?
- Limit antibiotics unless absolutely necessary
- Antibiotics do kill bad bacteria, but they also kill good bacteria in the digestive tract. Studies indicate that it may take up to 6 months for the microbiome to recover after antibiotics, if not longer12
- Watch your diet
- Eat more variety. Studies show, the more variety in your diet- the more diversity in your microbiota15.
- Eat lots of fruits and veggies as well as beans, legumes, and whole grains if tolerated. Diets rich in fiber provide food for the gut bacteria to help them grow health
- Eat fermented foods. I usually recommend to aim for at least ¼ cup of something fermented daily (sauerkraut, kimchi, kefir, etc).
- Be careful with too much sugar, especially refined sugars. Consuming high sugar diets allow certain bad bacteria to grow16.
- Avoid overconsumption of alcohol and artificial sweeteners. These can alter your microbiome18.
- Make stress reduction a priority
- High levels of stress can alter the structure of the intestinal barrier leading to an increased risk of imbalanced flora. Focusing on stress reduction is an important way to ensure microbiome health. My favorite ways to focus on stress reduction include meditation and restorative yoga.
- This also includes being mindful while you are eating. Eating in a stressed and hurried state (ex: while you’re driving) can impair digestion and lead to more undigested foods in your system.
- While you’re at it- go pet some animals. Studies show that people with animals have more diverse microbiome19.
If you do suspect an imbalance in your microbiome, talk to your doctor or your dietitian.